PHD, Kent State University, 2022, College of Arts and Sciences / Materials Science Graduate Program

Three-dimensional (3-D) tissue scaffolds produce suitable environments for cell growth and proliferation for longer periods of time compared to traditional two-dimensional (2-D) tissue culture and, act as appropriate models for the study of cell-cell/cell-scaffold interactions. 3-D models also allow to study cell activities and their functions as well as to evaluate diseases or tissue damage. Liquid crystal elastomers (LCEs) have intrinsic anisotropy and have shown to promote cell alignment and orientation and the presence of liquid crystals (LCs) at a molecular level with and without the use of external stimuli. The work presented in this thesis is the synthesis, design, and creation of 3-D LCEs scaffolds that support several cell lines to promote tissue regeneration. LCEs scaffolds have shown to meet all tissue scaffold requirements to support cell proliferation and growth since they can potentially be biocompatible, biodegradable and their properties, such as porosity and mechanical properties, can be tuned to adapt and match to different cell lines to obtain a suitable tissue. To tune porosity size and density, a salt leaching method was used. Cellulose nanocrystals (a biocompatible additive) were used as an additive to tune the mechanical properties of LCEs to match the young modulus of specific tissues. Once 3-D LCE scaffolds were produced to specifically match neural-like cell lines, we proceed to co-culture neuroblastoma and a glial cell lines (oligodendrocytes). When neuroblastomas are in presence of oligodendrocytes, myelin sheet is formed around the axon of neurons. We observed myelination of neurons during our co-culturing efforts allowing us to study its formation well over several weeks. Our findings will lead researchers on brain degenerative diseases such as Multiple Sclerosis (MS) to have a more appropriate model to quantify, monitor, and find treatments for demyelination and myelination of neurons. Last but not least, in this thesis we will sho (open full item for complete abstract)

Committee: Elda Hegmann (Advisor); Elda Hegmann (Committee Chair); Robert Clements (Committee Member); Richard Piet (Committee Member); Jennifer McDonough (Committee Member); Edgar Kooijman (Committee Member); Torsten Hegmann (Committee Member) Subjects: Materials Science

PHD, Kent State University, 2018, College of Arts and Sciences / Department of Physics

I investigate three systems that exhibit complex patterns in orientational order, which are controlled by geometry interacting with the dynamics of phase transitions, metastability, and activity. 1. Liquid Crystal Elastomers: Liquid-crystal elastomers are remarkable materials that combine the elastic properties of cross-linked polymer networks with the anisotropy of liquid crystals. Any distortion of the polymer network affects the nematic order of the liquid crystal, and, likewise, any change in the magnitude or direction of the nematic order influences the shape of the elastomer. When elastomers are prepared without any alignment, they develop disordered polydomain structures as they are cooled into the nematic phase. To model these polydomain structures, I develop a dynamic theory for the isotropic-nematic transition in elastomers. 2. Active Brownian Particles: Unlike equilibrium systems, active matter is not governed by the conventional laws of thermodynamics. I perform Langevin dynamics simulations and analytic calculations to explore how systems cross over from equilibrium to active behavior as the activity is increased. Based on these results, I calculate how the pressure depends on wall curvature, and hence make analytic predictions for the motion of curved tracers and other effects of confinement in active matter systems. 3. Skyrmions in Liquid Crystals: Skyrmions are localized topological defects in the orientation of an order parameter field, without a singularity in the magnitude of the field. For many years, such defects have been studied in the context of chiral liquid crystals—for example, as bubbles in a confined cholesteric phase or as double-twist tubes in a blue phase. More recently, skyrmions have been investigated extensively in the context of chiral magnets. In this project, I compare skyrmions in chiral liquid crystals with the analogous magnetic defects. Through simulations based on the nematic order tensor, I model both isolated skyrmions (open full item for complete abstract)

Committee: Jonathan Selinger (Advisor); John Portman (Committee Co-Chair) Subjects: Physics

Doctor of Philosophy, University of Akron, 2015, Polymer Science

Linear poly(styrene-b-isobutylene-b-styrene) (l-SIBS) and arborescent poly(styrene-b-isobutylene-b-styrene) (arb-SIBS) are a type of polyisobutylene-based thermoplastic elastomers (PIB-based TPE) characterized by an excellent mechanical, thermal and chemical stability, low permeability and excellent biostability and biocompatibility. PIB-based TPE are prepared by living carbocationic polymerization with sequential monomer addition which allows to obtain narrow molecular weight distribution and to synthesize a wide variety of architectures. These materials have been extensively used for biomedical applications, however they have a unique combination of properties, not available in any other TPE, that make them suitable for potential uses in other areas as well. This work reports the evaluation of three new potential technological applications for l-SIBS and arb-SIBS. In the first part of this work a new method for the preparation of a flexible piezoelectric polymer by incorporating a bent-core liquid crystal (BLC) in a PIB-based TPE, l-SIBS was shown. The polymer composite material containing 10 wt. % of BLC showed a piezoelectric charge constant d33 (~1 nm V-1) greater than commercially available piezoelectric ceramics. Small angle X-ray scattering (SAXS) results show that the liquid crystal–polymer composite becomes aligned during compression molding leading to macroscopic polarization without electric poling. In the second part of this work l-SIBS and arb-SIBS were sulfonated to prepare block copolymer ionomers. The materials were successfully sulfonated to various sulfonation degrees (SD), and characterized for water uptake and ionic conductivity. This modification significantly increased water uptake of both S-l-SIBS and S-arb-SIBS; the associated proton conductivity of the S-l-SIBS increased with the SD, however it did not rise at the desirable levels. For the S-arb-SIBS low values of proton conductivity were obtained, possibly due to the limited solub (open full item for complete abstract)

Committee: Judit E. Puskas Dr (Advisor); Gary R. Hamed Dr. (Committee Member); Mesfin Tsige Dr. (Committee Member); Darrell H. Reneker Dr. (Committee Member); Thein Kyu Dr. (Committee Member) Subjects: Materials Science; Polymer Chemistry; Polymers

Doctor of Philosophy, The Ohio State University, 2024, Chemical Engineering

Shape memory polymers (SMPs) have seen increased use in soft robotics, actuators, drug delivery, and optics because of their ability to respond to external stimuli in a variety of ways. As a representative class of shape memory polymers, liquid crystal elastomers (LCEs) have seen expanded interest in recent years, owing to their unique ability to reversibly deform to stimuli without the need for outside deformations. LCEs rely on liquid crystals (LCs), which are self-aligning, rod-like molecules that exhibit a phase between solids and liquids, for their unique reversibility. There is an opportunity to increase the usefulness of LCEs through copolymerization and the addition of nanostructures on the surface. In addition, traditional LCEs are hampered in some applications, namely biomedical applications, because of the inherent danger many of them pose to cells. This work seeks to improve LCEs in three main ways: copolymerizing LC monomers, creating nanoscopic surface structures, and templating the LC order into non-LC monomers. By copolymerizing different LC monomers together, we were able to provide a new avenue to control the magnitude and direction of LCE deformations. With the addition of densely packed, nanoscopic surface structures, we enhanced the adhesive force of LCE films increasing their utility in soft robotics. Finally, by templating the order of LCs to non-LC monomers, we created LCE-like materials that exhibit kinetically trapped, reversible deformations with polymers that are better suited for biomedical applications. These three thrusts have expanded the design space for LCEs and have introduced new materials and physical properties.

Committee: Xiaoguang Wang (Advisor); Lisa Hall (Committee Member); Stuart Cooper (Committee Member) Subjects: Chemical Engineering

Master of Science (M.S.), University of Dayton, 2023, Mechanical Engineering

Adaptive materials with programmable surface topography control can be utilized for selective boundary-layer tripping. Liquid crystal elastomers (LCE) have lately gained significant attention to be leveraged to enable these changes via repeatable and controlled out-of-plane deformations. The LCE can be preferentially aligned with circumferential patterns through the thickness of the film, which yields a predictable conical out-of-plane deformation when thermally activated. These reversible and predictable deployments can be utilized to develop a multifunctional surface designed for bodies in flow. This thesis concentrates on the experimental research of LCE behavior for purposes of active flow control via controlled surface topography. First, the deformations of the 12.7-mm diameter patterned LCE samples were characterized using digital image correlation in a controlled pressure chamber under positive and negative gauge pressures. The LCE's performance was highly dependent upon boundary conditions, specimen dimensions, and imprinted defect location relative to the boundary conditions, thus leading to the refinement of the LCE formulation to allow for a higher modulus. Then, to exhibit the potential for flow control, varying arrangements of representative topographical features were 3D-printed and characterized in a preliminary wind tunnel experiment using particle image velocimetry (PIV). Results demonstrated that a two-row arrangement of 1.5-mm feature height produced an asymmetric wake about a 73-mm cylinder, reducing drag while generating lift. Subsequently, a proof of concept model with active LCE elements was fabricated and tested using a force-balance instead of PIV in a wind tunnel. The results of the conceptual model demonstrated that LCEs exhibit the necessary performance to be used in flow control applications.

Committee: Richard Beblo Ph.D (Advisor); Siddard Gunasekaran Ph. D (Committee Member); Gregory Reich Ph. D (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Materials Science; Mechanical Engineering

PHD, Kent State University, 2023, College of Arts and Sciences / Materials Science Graduate Program

This dissertation describes stimuli-responsive liquid crystals and elastomers including thermal/electro-active ionic liquid crystal elastomers, UV responsive twist bend nematic liquid crystal dimmers and fast-switching chiral ferroelectric nematic liquid crystals with detailed studies on its nanoscale structures, electrical and optical properties for possible electric, optical and electro-optical applications. In this dissertation, the first preparation, physical properties, and electric bending actuation of a new class of active materials - ionic liquid crystal elastomers (iLCEs) are described. iLCEs can be actuated by low frequency AC or DC voltages of less than 1 V. The bending strains of the not optimized first iLCEs are already comparable to the well-developed ionic electroactive polymers (iEAPs). Additionally, iLCEs exhibit several novel and superior features. For example, pre-programmed actuation can be achived by patterning the substrates with different alignment domains at the level of cross-linking process. Since liquid crystal elastomers are also sensitive to magnetic fields, and can also be light sensitive, in addition to dual (thermal and electric) actuations in hybrid samples, iLCEs have far-reaching potentials toward multi-responsive actuations that may have so far unmatched properties in soft robotics, sensing and biomedical applications. The following two works are the understanding of the structure of the twist-bend nematic (NTB) phase. The first work presents hard and tender resonant X-ray scattering studies of two novel sulfur containing dimer materials for which we simultaneously measure the temperature dependences of the helical pitch and the correlation length of both the helical and positional order. In addition to an unexpected strong variation of the pitch with the length of the spacer connecting the monomer units, we find that at the transition to the NTB phase the positional correlation length drops. In the second work we use tender (open full item for complete abstract)

Committee: Antal Jakli (Committee Chair); Robin Selinger (Committee Member); Robert Clements (Committee Member); Robert Twieg (Committee Member); Deng-Ke Yang (Committee Member) Subjects: Materials Science; Nanotechnology; Optics; Physical Chemistry; Physics

PHD, Kent State University, 2022, College of Arts and Sciences / Department of Physics

Over the past few decades, there has been tremendous development on soft materials in soft robotics, energy generation and sensing applications. These soft materials are mostly polymers. Their compliant elasticity, good adaptability to external constraints, and biocompatibility make them suitable for those applications. Further, polymers that respond by changing their shape or size to an external stimulus such as electric field, magnetic field, heat, pressure, pH, and light have great potential for these applications. Among these stimuli responsive materials, electro responsive polymers (electroactive polymers (EAPs)) acquires great attention. Organic electrochemical transistors (OECTs) have attracted great attention since their discovery in 1984 due to their flexibility, biocompatibility, easy fabrication and tunability through synthetic chemistry. As OECTs conduct both electronic and ionic charge, they are suitable for bioelectronic applications, such as recording electric activity of cells and tissues, detection of ions, metabolites, antigens related with various diseases, hormones, DNA, enzymes and neurotransmitter. In my dissertation, I will describe how we developed ionic electroactive polymers (iEAPs) and ionic liquid crystal elastomers (iLCEs) for the applications of soft robotics, energy harvesting (flexo-ionic effect), sensing and organic electrochemical transistors. Firstly, we engineered poly (ethylene glycol) diacrylate based iEAPs for soft robotics application. Here, low voltage induced bending (converse flexoelectricity) of crosslinked poly (ethylene glycol) diacrylate (PEGDA), modified with thiosi-loxane (TS) and ionic liquid (1-hexyl-3-methylimidazolium hexafluorophos-phate) (IL) is studied. In between 2μm PEDOT:PSS electrodes at 1 V, it provides durable (95% retention under 5000 cycles) and relatively fast (2 s switching time) actuation with the second largest strain observed so far in iEAPs. In between 40 nm gold electrodes under 8 V DC volt (open full item for complete abstract)

Committee: Antal Jákli (Advisor); Björn Lüssem (Committee Member); Songping Huang (Committee Member); John West (Committee Member); Robin Selinger (Committee Member) Subjects: Physics

PHD, Kent State University, 2015, College of Arts and Sciences / Chemical Physics

In this work light- and heat-induced deformations in liquid crystal elastomers (LCEs) are studied and effects of external stress on the internal structure of LCEs are investigated. The studies are carried out for siloxane based side chain nematic LCEs. The internal structure of LCEs at the micron scale is probed via polarized light scattering during polymerization of the LCE network, showing variations of length scale of approximately 2 microns and the formation of domains with uniform orientation of the director. Simple modeling shows that the experimentally observed scattering can be produced by an in-plane director variation consistent with a domain-like structure of the director profile. Light induced shape changes in monodomain and polydomain LCEs are studied by means of nonlinear optical reflection. Temperature and polarization dependence of the light induced deformations is investigated, suggesting that in the studied materials the primary contribution to the induced deformation originates from laser heating rather than from photoisomerization of azo-dyes. Perturbation analysis is performed, predicting a micron scale surface protrusions consistent with the experimental observations. Numerical modeling of the LCE elastic response to local heating is carried out. The numerical model provides reasonable agreement with experimental observations, and demonstrates the effect of the soft deformation mode on the shape of the induced surface relief.

Committee: Peter Palffy-Muhoray Dr. (Committee Chair); Hiroshi Yokoyama Dr. (Committee Member); Jonathan V. Selinger Dr. (Committee Member); Xiaoyu Zheng Dr. (Committee Member); Michael Tubergen Dr. (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2012, Mechanical Engineering

Smart materials have significantly varied properties and their various types are used broadly in many different engineering applications. In order to grow the field and promote its long term viability, it is important to develop tools which enable researchers and practitioners to determine the best smart material for the application. Computerized material selection databases and systems have been recently developed by design and materials engineers to help users select the best materials for an application. However, documentation of smart materials is limited, especially for those aimed at the use of these materials in devices and applications. In this dissertation, system-level simulation models and collected material data are compiled in a GUI-based computer software called Polymers and Smart Materials Software (PSMS). This material selection tool encompasses material properties and material-level models as well as systems level smart material applications for a wide range of smart materials. This type of compiled data can expedite the material selection process when designing smart material based systems by allowing one to choose the most effective material for the application. The PSMS tool consists of the following three major sections: 1) Polymers (Polymer types and properties, Polymeric behaviors including dielectric and liquid crystal elastomers); 2) Smart Materials (Piezoelectric Ceramics/Polymers, Shape Memory Alloys/Polymers, Thermoelectrics, Electrorheological and Magnetorheological Fluids); 3) More information (External databases, Cost information, etc.). The software tool offers a wide variety of design and selection features. Material property and performance charts are provided to compare material properties and to choose the best material for optimal performance. The tool is also flexible in that it enables users to categorize material properties and create their own databases. In areas where existing models were inadequate for systems level integra (open full item for complete abstract)

Committee: Gregory Washington (Advisor); Marcelo Dapino (Advisor); Carlos Castro (Committee Member); Mark Walter (Committee Member) Subjects: Mechanical Engineering